title: Association of semen quality and occupational factors: comparison of case-control analysis and analysis of continuous variables.
abstract: OBJECTIVE
  To compare two statistical approaches, case-control and analysis of continuous parameters of semen, in examining the relationship between occupational exposures and male reproductive function.
  
  
  METHODS
  Case-control study.
  
  
  METHODS
  Males providing semen samples at a university infertility clinic.
  
  
  METHODS
  Nonvasectomized males who provided at least one semen sample at an infertility clinic.
  
  
  METHODS
  Standard clinical semen analysis.
  
  
  RESULTS
  Analyses using a dichotomous dependent variable did not uncover significant associations between any occupational factor and infertility case status. However, linear models incorporating continuous variables identified a number of occupational factors that were associated with specific parameters of semen. A reduction in percentage of progressive sperm and an increase in percentage of coiled tail sperm defects in welders, compared with unexposed subjects, were found. Significant dose-response relationships between level of perceived job stress and percentage of progressive sperm, total motile count, morphology, abnormal heads, and coiled tail defects were found.
  
  
  CONCLUSIONS
  The findings suggest that subtle changes in semen variables, possibly associated with workplace exposure, may be detected only with parametric analyses of continuous variables of semen.
authors.affiliation: Department of Community Health Sciences, The University of Calgary, Faculty of Medicine, Alberta, Canada. pbigelow@lamar.colostate.edu
authors.forename: P L
authors.initials: PL
authors.lastname: Bigelow
authors.forename: J
authors.initials: J
authors.lastname: Jarrell
authors.forename: M R
authors.initials: MR
authors.lastname: Young
authors.forename: T J
authors.initials: TJ
authors.lastname: Keefe
authors.forename: E J
authors.initials: EJ
authors.lastname: Love
mesh_terms: D000328:Adult; D000368:Aged; D016022:Case-Control Studies; D006801:Humans; D007248:Infertility, Male / Q000209:etiology* / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D009790:Occupations; D012661:Semen / Q000502:physiology*; D013223:Statistics as Topic / Q000379:methods; D013312:Stress, Physiological / Q000503:physiopathology; D011795:Surveys and Questionnaires